Sensor assembly for use in a security alarm system and method of installing the same

ABSTRACT

There is provided a method of installing a magnetic proximity sensor including positioning the magnetic field sensor in a desired location and positioning a magnet in a desired location relative to the magnetic field sensor, with an indicator of the sensor continuing to be turned on during the predetermined period of time when the magnetic field generated by the magnet is sensed by the magnetic field sensor, and being turned off during the predetermined period of time when the magnetic field generated by the magnet is not sensed by the magnetic field sensor. The indicator light thus assists in determining proper relative positioning of the magnet and the magnetic field sensor. If after the predetermined period of time more time is needed to install the magnetic proximity sensor, the method includes initiates another predetermined period of time by removing and replacing a lid of the magnetic proximity sensor.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a sensor assembly and, in particular,to a magnetic field sensor with an indicator which indicates thepresence or absence of a magnetic field or, to a security alarm sensorwith an RFID reader which indicates when the sensor is within apredetermined distance of an RFID tag.

Description of the Related Art

It is known to provide a magnetic field sensor with a light-emittingdiode indicator. U.S. Pat. No. 4,296,410, which issued on Oct. 20, 1981to Higgs et al., discloses an integrated circuit including a Hallelement and a threshold detector. The threshold detector is encased in aplastic housing with the plane of the Hall element parallel with a faceof the housing to provide a two-state Hall element proximity sensor. Alight-emitting diode is mounted in the housing and is connected to theoutput of the detector. This provides visual indication of the state ofthe sensor. A kit includes the sensor and a compatible magnet which maybe used as a proximity sensor in a security alarm system,

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a magnetic fieldsensor having an indicator which indicates the presence or absence of amagnetic field, or a security alarm sensor with an RFID reader whichindicates when the sensor in communication range with an RFID tag.

There is accordingly provided a magnetic field sensor comprising amicroprocessor and an indicator which turns on when a magnetic field issensed and turns off when a magnetic field is not sensed. Themicroprocessor renders the indicator inoperable a predetermined periodof time after the magnetic field sensor is powered up.

There is also provided a magnetic proximity sensor including a magnetwhich generates a magnetic field and a magnetic field sensor. Themagnetic field sensor comprises a microprocessor and an indicator whichturns on when a magnetic field generated by the magnet is sensed andturns off when a magnetic field generated by the magnet is not sensed.The microprocessor renders the indicator inoperable a predeterminedperiod of time after the magnetic field sensor is powered up.

There is further provided a magnetic field sensor comprising a housinghaving a lid. The magnetic field sensor includes a tamper switch whichdetects when the lid of the housing is opened. The magnetic field sensorincludes a device which senses a presence or an absence of a magneticfield. The magnetic field sensor includes a power source disposed withinthe housing. The magnetic field sensor includes a pull strip positionedto inhibit the power source from providing power to the magnetic fieldsensor. The magnetic field sensor is powered up when the pull strip isremoved from the power source. The magnetic field sensor includes amicroprocessor. A signal is sent by the tamper switch to themicroprocessor when the lid of the housing is open. A signal is sent bythe device to the microprocessor when a magnetic field is sensed. Themagnetic field sensor includes an indicator which indicates the presenceor the absence of a magnetic field. The power source supplies current tothe indicator, and the indicator turns on when a magnetic field issensed and turns off when a magnetic field is not sensed. The indicatoris initially operable following the pull strip being removed from thepower source and the magnetic field sensor being powered up. Themicroprocessor renders the indicator inoperable a predetermined periodof time after the pull strip is removed from the power source and themagnetic field sensor is powered up. The indicator remains inoperableuntil the lid of the housing is removed and the lid of the housing isclosed at which point the indicator is operable until the microprocessorrenders the indicator inoperable a predetermined period of time afterthe lid of the housing is closed.

There is yet also provided a proximity sensor including a magnet whichgenerates a magnetic field and a magnetic field sensor. The magneticfield sensor includes a housing having a lid. The magnetic field sensorincludes a tamper switch which detects when the lid of the housing isopened. The magnetic field sensor includes a device which senses apresence or an absence of a magnetic field. The magnetic field sensorincludes a power source disposed within the housing. The magnetic fieldsensor includes a pull strip positioned to inhibit the power source fromproviding power to the magnetic field sensor. The magnetic field sensoris powered up when the pull strip is removed from the power source. Themagnetic field sensor includes a microprocessor. A signal is sent by thetamper switch to the microprocessor when the lid of the housing is open.A signal is sent by the device to the microprocessor when a magneticfield is sensed. The magnetic field sensor includes an indicator whichindicates the presence or the absence of a magnetic field. The powersource supplies current to the indicator, and the indicator turns onwhen a magnetic field is sensed and turns off when a magnetic field isnot sensed. The indicator is initially operable following the pull stripbeing removed from the power source and the magnetic field sensor beingpowered up. The microprocessor renders the indicator inoperable apredetermined period of time after the pull strip is removed from thepower source and the magnetic field sensor is powered up. The indicatorremains inoperable until the lid of the housing is removed and the lidof the housing is closed at which point the indicator is operable untilthe microprocessor renders the indicator inoperable a predeterminedperiod of time after the lid of the housing is closed.

There is yet further provided a method of installing a magneticproximity sensor. The magnetic proximity sensor includes a magnet. Themethod includes providing the magnetic proximity sensor with anindicator that turns on for a predetermined period of time when amagnetic field generated by the magnet is sensed by the magnetic fieldsensor. The method includes positioning the magnetic field sensor in adesired location and positioning the magnet in a desired locationrelative to the magnetic field sensor. The indicator continues to beturned on during said predetermined period of time when the magneticfield generated by the magnet is sensed by the magnetic field sensor.The indicator is turned off during the predetermined period of time whenthe magnetic field generated by the magnet is not sensed by the magneticfield sensor. The indicator light thus assists in determining properrelative positioning of the magnet and the magnetic field sensor. Ifafter the predetermined period of time more time is needed to installthe magnetic proximity sensor, the method includes initiating anotherpredetermined period of time by removing and replacing a lid of themagnetic proximity sensor.

In one example, the indicator may be a light-emitting diode. The powersource may be a coin cell battery. The magnetic field sensor may includea supercapacitor. The magnetic field sensor may also include a tamperswitch.

The sensors disclosed herein may be used together with a magnet as aproximity sensor, for example, as a door sensor or window sensor in asecurity alarm system.

There is yet additionally provided a security alarm sensor assemblycomprising an RFID tag mountable on a first of a window or a door orframing thereof. The security alarm sensor assembly includes a sensormountable on a second of the window or the door or said framing thereof.The sensor includes a housing having a lid. The sensor includes a tamperswitch which detects when the lid of the housing is opened. The sensorincludes a power source disposed within the housing. The sensor includesan RFID reader which emits an electromagnetic field. The sensor includesa microprocessor. A signal is sent by the tamper switch to themicroprocessor when the lid of the housing is open. The microprocessoranalyzes changes in signals from the RFID tag to determine when adistance between the RFID tag and the RFID reader is within apredetermined threshold. The sensor includes an indicator whichindicates when the distance between the RFID tag and the RFID reader iswithin said predetermined threshold. The power source supplies currentto the indicator. The indicator turns on when the distance between theRFID tag and the RFID reader is within said predetermined threshold. Theindicator turns off when the distance between the RFID tag and the RFIDreader is outside of said predetermined threshold. The indicator isinitially operable upon the sensor being powered up. The microprocessorrenders the indicator inoperable a predetermined period of time afterthe sensor being powered up. The indicator remains inoperable until thelid of the housing is removed and the lid of the housing is next closedat which point the indicator is operable until the microprocessorrenders the indicator inoperable a predetermined period of time afterthe lid of the housing is closed.

BRIEF DESCRIPTIONS OF DRAWINGS

The invention will be more readily understood from the followingdescription of the embodiments thereof given, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a sensor assembly according to a firstaspect, the sensor assembly comprising a magnet and a first magneticfield sensor;

FIG. 2 is another perspective view of the magnet and the magnetic fieldsensor of FIG. 1;

FIG. 3 is a further perspective view of the magnet and the magneticfield sensor of FIG. 1;

FIG. 4 is an exploded view of the magnet and the magnetic field sensorof FIG. 1;

FIG. 5 is a schematic diagram of the magnetic field sensor of FIG. 1;

FIG. 6 is a bottom plan view of the magnetic field sensor of FIG. 1;

FIGS. 7A to 7E are circuit diagrams of the magnetic field sensor of FIG.1;

FIG. 8 is a perspective view showing the magnet and the magnetic fieldsensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window closed;

FIG. 9 is another perspective view showing the magnet and the magneticfield sensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window closed;

FIG. 10 is a further perspective view showing the magnet and themagnetic field sensor of FIG. 1 being used as a window sensor in asecurity alarm system with the window closed;

FIG. 11 is a perspective view showing the magnet and the magnetic fieldsensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window opened a distance D1;

FIG. 12 is another perspective view showing the magnet and the magneticfield sensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window opened a distance D1;

FIG. 13 is a further perspective view showing the magnet and themagnetic field sensor of FIG. 1 being used as a window sensor in asecurity alarm system with the window opened a distance D1;

FIG. 14 is a perspective view showing the magnet and the magnetic fieldsensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window opened a distance D2;

FIG. 15 is another perspective view showing the magnet and the magneticfield sensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window opened a distance D2;

FIG. 16 is a further perspective view showing the magnet and themagnetic field sensor of FIG. 1 being used as a window sensor in asecurity alarm system with the window opened a distance D2;

FIG. 17 is a perspective view showing the magnet and the magnetic fieldsensor of FIG. 1 being used as a window sensor in a security alarmsystem with the window opened a distance D3;

FIG. 18 is a flow chart showing the logic of installing the magnet andthe magnetic field sensor of FIG. 1 relative to each other;

FIG. 19 is a flow chart showing the logic of a software algorithm whichdrives the magnetic field sensor of FIG. 1;

FIG. 20 is a perspective view of a sensor assembly according to a secondaspect, the sensor assembly comprising a magnet and a magnetic fieldsensor;

FIG. 21 is another perspective view of the magnet and the magnetic fieldsensor of FIG. 20;

FIG. 22 is a perspective view of a sensor assembly according to a thirdaspect, the sensor assembly comprising a magnet and a magnetic fieldsensor;

FIG. 23 is a perspective view of a sensor assembly according to a fourthaspect, the sensor assembly comprising a magnet and a magnetic fieldsensor;

FIG. 24 is a perspective view of a sensor assembly according to a fifthaspect, the sensor assembly comprising a magnet and a magnetic fieldsensor;

FIG. 25 is a front, right side exploded view of a sensor assemblyaccording to a sixth aspect, the sensor assembly comprising a magnet anda magnetic field sensor, with a door frame and door to which the magnetfield sensor and magnet are to be connected also being shown, the doorframe and door being shown in fragment;

FIG. 26 is a rear, left side perspective view of the magnetic fieldsensor of FIG. 25, with a pull strip thereof in the process of beingremoved to enable a power source thereof to power the magnetic fieldsensor;

FIG. 27 is a flow chart showing the logic of installing the magnet andthe magnetic field sensor of FIG. 25 relative to each other;

FIG. 28 is a flow chart showing the logic of a software algorithm whichdrives the magnetic field sensor of FIG. 1;

FIG. 29 is a perspective view of a sensor assembly according to aseventh aspect, the sensor assembly comprising an RFID tag and a sensorwith an RFID reader, the sensor being shown in a perspective, explodedview;

FIG. 30 is a perspective view showing the RFID tag and the sensor ofFIG. 29 being used as a window sensor in a security alarm system withthe window closed;

FIG. 31 is a perspective view showing the RFID tag, the sensor and thewindow of FIG. 30 with the window being open a distance of D1.6;

FIG. 32 is a perspective view showing the RFID tag, the sensor and thewindow of FIG. 30, the window being open a distance of D2.6; and

FIG. 33 is a rear, left side perspective view of a sensor assemblyaccording to an eighth aspect, the sensor assembly being similar to thatshown in FIG. 29 with the exception that the sensor assembly includes apull strip with the removal thereof enabling a power source thereof topower the sensor thereof.

DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

Referring to the drawings and first to FIGS. 1 to 3, there is a provideda sensor assembly 9. The sensor assembly includes a first subassembly,in this embodiment in the form of a magnet 10. The sensor assembly 9includes a second subassembly, in this embodiment a sensor, in thisexample a magnetic field sensor 14. A field, in this example a magneticfield 12, is generated by the magnet 10 and said magnetic field issensed by the magnetic field sensor.

The magnetic field sensor 14 includes an indicator which, in thisexample, is a visual indicator in the form of an indicator light 16 thatturns on when the magnetic field sensor 14 is within the magnetic field12 as shown in FIGS. 1 and 2. The indicator light 16 turns off when themagnetic field sensor 14 is outside the magnetic field 12 as shown inFIG. 3. The indicator light 16 may accordingly provide a visualindication as to the presence or absence of a magnetic field. Togetherwith magnet 10 and magnetic field sensor 14 may be used as a magneticproximity sensor.

The magnet 10 is shown in greater detail in FIG. 4 and, in this example,is a bar magnet 11 which is disposed in a housing 13 provided with acover 15. The magnetic field sensor 14 is also shown in greater detailin FIG. 4 and, in this example, is a substantially rectangularparallelepiped with rounded corners but may be other shapes. Themagnetic field sensor 14 includes a housing 18 and a circuit board 20disposed within the housing. The housing 18 is provided with a lid 19that has a window 21 to facilitate viewing of the indicator light 16which is mounted on the circuit board 20. The window 21 may be anaperture in the lid 19 or a translucent portion of the lid 19. Amicroprocessor 22, a power source which is in the form of a coin cellbattery 24, and a device which senses a magnetic field which is in theform of a reed switch 26 are also mounted on the circuit board 20. Itwill however be understood by a person skilled in the art that any AC orDC power source may be used. Likewise any device which senses a magneticfield, such as a magnetoresistive sensor or Hall Effect sensor orMAGNASPHERE™ may be used in place of the reed switch.

In this example, the indicator light 16 is a light-emitting diodepackage and includes a blue light-emitting diode, a green light-emittingdiode, and a red light-emitting diode. The reed switch 26 is actuated bya magnetic field and the microprocessor 22 monitors the change of stateof the reed switch 26 by periodically sampling the reed switch 26 tosense a magnetic field. If a magnetic field is sensed then themicroprocessor 22 turns on the indicator light 16. In the absence of amagnetic field, the microprocessor 22 turns the indicator light 16 off.The sampling of the reed switch 26 by the microprocessor 22 may be done,for example, four times per second or as many times per second asrequired. The sensitivity of the magnetic field sensor 14 may beadjusted by selecting different types of reed switches. This may be usedto set a maximum or minimum distance at which the magnetic field sensor14 is able to sense a magnet. If another device which senses a magneticfield is used in the magnetic sensor, such as a magnetoresistive sensoror Hall Effect sensor or MAGNASPHERE™, then the sensitivity of themagnetic field sensor may be adjusted based on measured analog and/ordigital output.

Referring now to FIG. 5, in this example, the magnetic field sensor 14includes a radio, which is in the form of a radio chip 28 in thisexample, and an antenna 30 that allows the magnetic field sensor 14 totransmit and receive radio signals. The antenna 30 may communicate witha control panel 40 as part of a security alarm system 31. There is alsoa battery detection circuit 32, a tamper switch 34, and a supercapacitor36. The battery detection circuit 32 and tamper switch 34 are bothconventional and in communication with the microprocessor 22. Thesupercapacitor 36 may be used to assist the coin cell battery 24 as thepower source. Without the supercapacitor 36 the coin cell battery 24 maynot be able to provide the surge current required when the radio chip 28and the antenna 30 transmit and receive radio signals. This is due tothe internal resistance of a coin cell battery. A coin cell batterygenerally cannot be used in applications requiring current in excess ofabout 20 to 30 milliamperes. The internal resistance of the coin cellbattery causes a voltage drop when larger currents are required. Thismay cause the terminal voltage to drop below a minimum acceptable levelof, for example, 2.2 volts.

The supercapacitor 36 may have a low profile which, in combination withuse of the coin cell battery 24, allows the magnetic field sensor 14 tobe relatively small. The supercapacitor 36 allows for high short termcurrent draws while still providing a terminal voltage of, for example,3.0 volts. Without the supercapacitor 36 a larger battery may have to beused as a power source. The supercapacitor 36 may have a sufficientresidual charge to prevent the microprocessor 22 from properly detectingthe removal of the coin cell battery 24 during battery replacement.However, the battery detection circuit 32 allows the microprocessor 22to shut down properly when the coin cell battery 24 is removed. Theremay also be a reverse voltage protection circuit 38, which may be adiode or P-channel mosfet, connected in series between the coin cellbattery 24 and the supercapacitor 36 to ensure that the coin cellbattery 24 is not reverse charged if the supercapacitor 36 has a highervoltage. The tamper switch 34 may be internal or external of the housing18 and detects when the lid 19 of the housing 18 is removed and sends asignal to the microprocessor that the lid 19 of the housing 18 has beenremoved and someone is tampering with the magnetic field sensor 14. Thetamper switch 34 also sends a signal to the microprocessor 22 to restartan algorithm related to the sensing of a magnetic field when the tamperswitch 34 detects that the lid 19 of the housing 18 has been removed. Inother examples, the magnetic field sensor may not have a tamper switchand the microprocessor may be signalled to restart the algorithm relatedto the sensing of a magnetic field when the coin cell battery isinserted. The microprocessor may alternatively be signalled to restartthe algorithm related to the sensing of a magnetic field when an ON/OFFswitch is actuated. Such an ON/OFF switch may be used turn the indicatoron and off.

The magnetic field sensor 14 is further provided in this example with aMEMS oscillator 42 which may be programmed to a plurality of discretefrequencies and, in this case, to at least four discrete frequencieswhich are feed to the radio chip 28 to generate an output frequencyranging between 250 MHz and 1 GHz. The MEMS oscillator 42 is able toprovide the at least four discrete frequencies to the radio chip 28without an additional phase locked loop being required to generate theoutput frequency, or output signal 41, because the radio chip 28 isprovided with a single phase-locked loop 29, for example, a x32multiplier to generate the output frequency. There is also a dip switch44 which, in this example, is a four position dip switch. Referring nowto FIG. 6, the dip switch 44 is mounted on a side of the circuit board20 opposite of the indicator light 16. This allows the dip switch 44 tobe accessed through an aperture 46 in the housing 18 as shown in FIG. 6.The M EMS oscillator and dip switch are not strictly required and themagnetic field sensor may not have such components in other embodiments.

The microprocessor 22 is programmed with a plurality of data protocolsand each output frequency may operate on at least one of the dataprotocols. The dip switch 44 is actuated to provide a code to themicroprocessor 22 and a data protocol is implemented by themicroprocessor 22 based on the code. The MEMS oscillator 42 isprogrammed to a discrete frequency based on the data protocolimplemented by the microprocessor 22. The MEMS oscillator 42 thenprovides the discrete frequency to the radio chip 28 which an outputsignal 41 based on the discrete frequency. This allows an installer toselect a discrete frequency to match the protocol of a given alarmsystem. Respective ones of digitally tuned capacitor chips 48 a and 48 bare disposed at each terminal of the antenna 30. The capacitor chips 48a and 48 b are used in a shunt mode rather than a series mode to preventa degradation of antenna performance resulting due to stray capacitanceissues when the capacitor chips 48 a and 48 b are used in series. Usingthe capacitor chips 48 a and 48 b in a shunt configuration may allow theantenna 30 to be tuned. The supercapacitor 36 may maintain a maximumoutput signal by maintaining the voltage at its maximum value duringtransmission of the output signal. A circuit diagram of the magneticfield sensor is shown in FIGS. 7A to 7E.

Referring now to FIGS. 8 to 17, the magnet 10 and magnetic field sensor14 are shown in use as a proximity sensor in the form of a window sensorof a security alarm system. It will however be understood by a personskilled in the art that the magnet 10 and magnetic field sensor 14 mayalso be used as a door sensor or in any other proximity sensorapplication. The magnet 10 and magnetic field sensor 14 are each mountedon a window 50 with the magnetic field sensor 14 generally being mountedfirst, although this is not strictly required. The magnet 10 is mountedon a stile 52 of the window 50 while the magnetic field sensor 14 ismounted on a side jamb 54 of the window near a sill 56 thereof. Thewindow 50 is fully closed in FIGS. 8 to 10 with a bottom rail 58 of thewindow abutting the sill 56 thereof. When the window 50 is fully closed,the magnetic field sensor 14 is able to sense a magnetic field generatedby the magnet 10 when the magnet is mounted along the stile 52 asindicated by the indicator light 16 which is turned on in FIGS. 8 to 10.The indicator light 16 of the magnetic field sensor 14 is turned on whenthe magnet 10 is mounted on the stile 52 at a first position adjacent tothe bottom rail 58 of the window 50 as shown in FIG. 8, at a secondposition away from the bottom rail 58 of the window 50 as shown in FIG.9, and at a third position further away from the bottom rail 58 of thewindow 50 as shown in FIG. 10. This provides a visible confirmation toan installer that, when the magnetic field sensor 14 is mounted on theside jamb 54 of the window 50 near the sill 56 thereof, the magnet 10may be mounted anywhere on the stile 52 between the first position andthe third position for the magnetic field sensor to still be able tosense a magnetic field generated by the magnet. An alarm willaccordingly not be triggered when the window 50 is fully closed and themagnet 10 and magnetic field sensor 14 are positioned relative to oneanother as shown in FIGS. 8 to 10.

However, it may be desirable for an alarm to not be triggered when thewindow 50 is not fully closed. This would allow the window 50 to bepartially opened for ventilation but not enough to allow an intruder toenter through the window. For example, as shown in FIGS. 11 to 13, itmay be desired to allow the window 50 to be opened a distance of D1without triggering an alarm. FIG. 11 shows that the magnetic fieldsensor 14 is able to sense the magnetic field generated by the magnet10, as visually indicated by the indicator light 16 which is turned on,when the magnet 10 is mounted on the stile 52 adjacent to the bottomrail 58. FIG. 12 shows that the magnetic field sensor 14 is also able tosense the magnetic field generated by the magnet 10, as visuallyindicated by the indicator light 16 which is turned on, when the magnet10 is mounted on the stile 52 away from the bottom rail 58. FIG. 13shows that the magnetic field sensor 14 is unable to sense the magneticfield generated by the magnet 10, as visually indicated by the indicatorlight 16 which is turned off, when the magnet 10 is mounted on the stile52 further away from the bottom rail 58. The indicator light 16accordingly provides a visual indication to an installer as to where onthe stile 52 the magnet 10 may be mounted to allow the window 50 to beopened a distance of D1 without triggering an alarm.

FIGS. 14 to 16 show where the magnet 10 may be positioned to avoidtriggering an alarm when the window is opened a distance of D2 which isgreater than D1. FIG. 14 shows that the magnetic field sensor 14 is ableto sense a magnetic field generated by the magnet 10, as visuallyindicated by the indicator light 16 which is turned on, when the magnet10 is mounted on the stile 52 adjacent to the bottom rail 58. FIG. 15shows that the magnetic field sensor 14 is unable to sense the magneticfield generated by the magnet 10, as visually indicated by the indicatorlight 16 which is turned off, when the magnet 10 is mounted on the stile52 away from the bottom rail 58. FIG. 16 shows that the magnetic fieldsensor 14 is also unable to sense the magnetic field generated by themagnet 10, as visually indicated by the indicator light 16 which isturned off, when the magnet 10 is mounted on the stile 52 further awayfrom the bottom rail 58. The indicator light 16 accordingly provides avisual indication to an installer that the magnet 10 should be mountedon the stile 52 adjacent to the bottom rail 58, allowing the window 50to be opened a distance of D2 without triggering an alarm. However, asshown in FIG. 17, opening the window a distance of D3 which is greaterthan D2 will trigger an alarm even if the magnet 10 is mounted on thestile 52 adjacent to the bottom rail 58. The indicator light 16accordingly provides an installer with a visual indication to verifycorrect placement of the magnet 10 to allow a maximum threshold openingof the window 50. It will be understood by a person skilled in the artthat mounting the magnet 10 on the stile 52 of the window 50 andmounting the magnetic field sensor 14 on the side jamb 54 of the windowis only an example. The magnet 10 and the magnetic field sensor 14 maybe mounted anywhere provided there is relative movement of the magnet 10and the magnetic field sensor 14 when the window 50 is opened.

FIG. 18 is a flow chart showing the logic of installing the magnet 10and magnetic field sensor 14 relative to each other. In this embodimentthe coin cell battery 24 is first inserted into the magnetic fieldsensor 14, as shown by box 53. It is next determined if the indicatorlight flashes, as shown by box 55, to indicate that the magnetic fieldsensor 14 seen in FIG. 17 has powered up and is functioning properly. Ifthe indicator light 16 does not flash, then the magnetic field sensor 14is not functioning properly and the coin cell battery 24 is removed andreplaced, as shown by box 57 in FIG. 18.

Referring to FIGS. 8 and 18, the magnetic field sensor 14 is nextpositioned in a desired location, as shown by box 59, and the magnet 10positioned in a desired location relative to the magnetic field sensor14, as shown by box 61. It is next determined if the indicator lightturns on based on whether the magnet is within range, as shown by box63. The indicator light 16 will turn on when a magnetic field generatedby the magnet 10 is sensed by the magnetic field sensor 14, as seen inFIGS. 8 to 12 and 14 and the indicator light 16 will turn off when amagnetic field generated by the magnet 10 is not sensed by the magneticfield sensor 14, as seen in FIGS. 13 and 15 to 17. The indicator light16 accordingly assists an installer in determining proper relativepositioning of the magnet 10 and magnetic field sensor 14. This allowsthe window 50 to be opened a certain distance without triggering thealarm. Once the installer is satisfied with the relative positioning ofthe magnet 10 and magnetic field sensor 14 as shown by box 65 in FIG.18, the lid 19 of the magnetic field sensor 14 is closed, as shown bybox 67. The indicator light 16 will then remain on for a predeterminedperiod of time when a magnetic field generated by the magnet 10 issensed by the magnetic field sensor 14, as shown by box 69.

Referring to FIG. 4, the magnetic field sensor 14 is further providedwith software having an algorithm which turns off the indicator light 16after a predetermined period of time even if the magnetic field sensor14 senses a magnetic field. This conserves the coin cell battery 24 ofthe magnetic field sensor 14 and does away with any visual annoyanceresulting from the indicator light 16 being turned on when the window 50is closed or opened less than a maximum threshold opening required totrigger an alarm. Referring to FIGS. 8 and 13, the magnetic field sensor14 will however continue to otherwise operate normally and transmit asignal to trigger an alarm when the window 50 is opened and the magneticfield sensor 14 no longer senses a magnetic field generated by themagnet 10. The indicator light 16 is accordingly operable duringinstallation of the window sensor and assists an installer indetermining the relative positioning of the magnet 10 and magnetic fieldsensor 14 so as to allow the window 50 to be opened a certain distancewithout triggering the alarm. If an installer is unable to position themagnet 10 and magnetic field sensor 14 within the predetermined periodof time before the software turns off the indicator light 16 then thelid 19 of the magnetic field sensor 14 can be removed to restart thealgorithm. Replacing of the lid 19 will result in another predeterminedperiod of time in which the indicator light 16 is operable to assist aninstaller in determining the relative positioning of the magnet 10 andmagnetic field sensor 14 so as to allow the window 50 to be opened acertain distance without triggering the alarm.

FIG. 19 is a flow chart showing the logic of the algorithm. In thisembodiment the coin cell battery 24 seen in FIG. 4 is first insertedinto the magnetic field sensor 14, as shown by box 71 in FIG. 19.Referring to FIGS. 8 and 19 and as shown by box 73 the greenlight-emitting diode of the indicator light 16 thereafter turns on for aperiod of time, for example, five seconds. This indicates that themagnetic field sensor 14 has powered up and is functioning properly. Theblue light-emitting diode of the indicator light 16 will then beoperable, as shown by box 75. The magnet 10 and the magnetic fieldsensor 14 are next positioned relative to one another as shown in FIGS.7 to 16. The blue light-emitting diode of the indicator light 16 willturn on when a magnetic field generated by the magnet 10 is sensed bythe magnetic field sensor 14 and the blue light-emitting diode of theindicator light 16 will turn off when a magnetic field generated by themagnet 10 is not sensed by the magnetic field sensor 14. The indicatorlight 16 accordingly assists an installer in determining proper relativepositioning of the magnet 10 and magnetic field sensor 14. Properrelative positioning of the magnet 10 and magnetic field sensor 14 mayallow the window 50 to be opened a certain distance without triggeringthe alarm.

If an installer is unable to position the magnet 10 and magnetic fieldsensor 14 within the predetermined period of time before the softwareturns off the indicator light 16 then the lid 19 can be removed torestart the algorithm as shown in FIG. 18. Thus the magnetic fieldsensor determines if the lid thereof is open or still within thepredetermined period of time, as shown by box 77. If the predeterminedperiod of time has expired, the blue LED light is turned off, as shownby box 79 in FIG. 19. If the lid is open and then closed, thepredetermined period of time begins once more and it is next determinedwhether the magnetic field sensor senses a magnetic field, as shown bybox 81. If yes, the blue LED light will turn on as shown by box 83. Ifno magnetic field is sensed by the magnetic field sensor, the blue LEDlight remains off, as shown by box 85, and the positioning of themagnetic field sensor relative to the magnet will need to be adjusted.

A red light-emitting diode of the indicator light 16 will flash when thecoin cell battery 24 runs down below a predetermined low batterythreshold in this example. The frequency of the flashing will increaseas the battery continues to run down.

The software may run other routines as set out below during operation ofthe magnetic field sensor 14.

task 1:

-   -   if tamper switch active (lid open) now or within past three        minutes:        -   if magnet is present:            -   blue light-emitting diode ON        -   else            -   blue light-emitting diode OFF                task 2    -   if magnet becomes present or magnet becomes absent:        -   send magnet-change message            -   if battery is failing                -   blink red light-emitting diode            -   else                -   if tamper switch active (lid open) now or within                    past three minutes:                -    blink green light-emitting diode                    task 3:    -   if approximately one hour has passed with no message sent:        -   send supervisory message

FIGS. 20 to 21 show a sensor assembly 9.1 including a magnet 10.1 andmagnetic field sensor 14.1 according to a second aspect. Like parts havelike numbers and functions as the sensor assembly 9, magnet 10 andmagnetic field sensor 14.1 shown in FIGS. 1 to 19 with the addition ofdecimal extension “0.1”. Assembly 9.1 is substantially the same asassembly 9 shown in FIGS. 1 to 19 with the following exceptions.

Magnetic field sensor 14.1 has a first indicator light 16.1 and a secondindicator light 74. The first indicator light 16.1 functions in a mannersubstantially identical to the indicator light 16 of the magnetic fieldsensor 14 shown in FIGS. 1 to 19. The first indicator light accordinglyprovides a visual indication as to the presence or absence of a magneticfield. The second indicator light 74 provides a visual indication as tothe strength of a magnetic field. The first indicator light 16.1 turnson when the magnetic field sensor 14.1 is within the magnetic field 12.1generated by the magnet 10. However, as shown in FIG. 20, the secondindicator light 74 does not turn on when the magnetic field sensor 14.1is merely near a periphery of the magnetic field 12.1. The secondindicator light 74 only turns on when the magnetic field sensor 14.1 iswell within the magnetic field 12.1 as shown in FIG. 21. This allows aninstaller to see the best range for the relative positioning of themagnet 10.1 and magnetic field sensor 14.1. The second indicator light74 is turned on by a microprocessor when a second, parallel device suchas a reed switch senses a magnetic field.

FIG. 22 shows a sensor assembly 9.2 including a magnet 10.2 and magneticfield sensor 14.2 according to a third aspect. Like parts have likenumbers and functions as the sensor assembly 9, magnet 10 and magneticfield sensor 14 shown in FIGS. 1 to 19 with the addition of decimalextension “0.2”. Assembly 9.2 is substantially the same as assembly 9shown in FIGS. 1 to 1.9 with the following exceptions.

Magnetic field sensor 14.2 has a socket 84 for an additional drycontact. This allows another device, such as a reed switch 86, whichsenses the presence or absence of the magnetic field 12.2 generated bythe magnet 10.2, to be coupled to the magnetic field sensor 14.2 by atether 88. This increases the range of the magnetic field sensor 14.2 asthe indicator light 16.2 will turn on when the reed switch 86 is withinthe magnetic field 1.2.2 even if the magnetic field sensor 14.2 is notwithin the magnetic field 12.2.

The examples shown in FIGS. 1 to 22 comprise a magnetic field sensorwith an indicator in the form of an indicator light. However, it will beunderstood by a person skilled in the art that, in other examples, theindicator may be an auditory indicator which produces a sound toindicate the presence or absence of a magnetic field, or a vibratoryindicator which vibrates to indicate the presence or absence of amagnetic field, or a combination of indicators selected from a visualindicator, an auditory indicator and a vibratory indicator. A switch maybe used to select a desired indicator mode.

FIG. 23 shows a sensor assembly 9.3 including a magnet 10.3 and magneticfield sensor 14.3 according to a fourth aspect. Like parts have likenumbers and functions as the sensor assembly 9, magnet 10 and magneticfield sensor 14 shown in FIGS. 1 to 19 with the addition of decimalextension “0.3”. Assembly 9.3 is substantially the same as assembly 9shown in FIGS. 1 to 19 with the following exceptions.

Magnetic field sensor 14.3 includes an indicator in the form of anauditory indictor 16.3 that provides an auditory indication as to thepresence or absence of a magnetic field. The auditory indicator turns onand emits a sound when the magnetic field sensor 14.3 is within themagnetic field 12.3 generated by the magnet 10.3. This provides anauditory indication as to the presence of a magnetic field. However,after a predetermined period of time, the auditory indicator 16.3 willbe turned off even in the presence of the magnetic field 12.3. Thisconserves power and does away with any auditory annoyance when themagnetic field sensor 14.3 is part of a proximity sensor in a securityalarm system 31.3.

FIG. 24 shows a sensor assembly 9.4 including a magnet 10.4 and magneticfield sensor 14.4 according to a fifth aspect. Like parts have likenumbers and functions as the sensor assembly 9, magnet 10 and magneticfield sensor 14 shown in FIGS. 1 to 19 with the addition of decimalextension “0.4”. Assembly 9.4 is substantially the same as assembly 9shown in FIGS. 1 to 19 with the following exceptions.

Magnetic field sensor 14.4 includes an indicator in the form of avibratory indictor 16.4 that provides a vibratory indication as to thepresence or absence of a magnetic field. The vibratory indicator turnson and vibrates when the magnetic field sensor 14.4 is within themagnetic field 12.4 generated by the magnet 10.4. This provides avibratory indication as to the presence of a magnetic field. However,after a predetermined period of time, the vibratory indicator 16.4 willbe turned off even in the presence of the magnetic field 12.4. Thisconserves power and does away with any vibratory annoyance when themagnetic field sensor 14.4 is part of a proximity sensor in a securityalarm system 31.4.

FIGS. 25 to 28 show a sensor assembly 9.5 including a magnet 10.5 andmagnetic field sensor 14.5 according to a sixth aspect. Like parts havelike numbers and functions as the sensor assembly 9, magnet 10 andmagnetic field sensor 14 shown in FIGS. 1 to 19 with the addition ofdecimal extension “0.5”. Assembly 9.5 is substantially the same asassembly 9 shown in FIGS. 1 to 19 with the following exceptions.

As seen in FIG. 25, magnetic field sensor 14.5 includes an insulatingmember, in this example a flexible, planer, insulator strip, in thiscase a pull strip 90. The pull strip has a proximal end 92 disposedwithin the housing 18.5 and a distal end 94. The pull strip 90 extendsoutwards from the rear 96 of the housing in this example, from thedistal end thereof towards the proximal end thereof. The proximal end 92of the pull strip 90 is positioned to inhibit the power source, in thisexample battery 24.5, from providing power to the rest of the magneticfield sensor 14.5: the pull strip extends between the battery and therest of the circuitry of the magnified filed sensor and thereby inhibitselectrical connection therebetween. In this example the proximal end ofthe pull strip 90 removably couples to one of the terminals 98 of thebattery 24.5 via adhesive 95 seen in FIG. 25.

Referring to FIG. 26, an installer pulling on distal end 94 of the pullstrip, as shown by arrow 100, causes the pull strip to be removed andthereby causes the magnetic field sensor 14.5 to be powered up by thebattery 24.4 seen in FIG. 25. Still referring to FIG. 25, the indicator1.6.5 is initially operable following the pull strip 90 being removedfrom the power source and the magnetic field sensor 14.5 being poweredup, and the microprocessor 22.5 renders the indicator inoperable apredetermined period of time after the pull strip has been removed fromthe power source and the magnetic field sensor is powered up. Theindicator remains inoperable until the lid 19.5 of the housing 18.5 isremoved and the lid of the housing is closed once more at which pointthe indicator 16.5 is operable until the microprocessor 22.5 renders theindicator inoperable a predetermined period of time after the lid of thehousing is closed.

FIGS. 29 to 32 show a sensor assembly 9.6 according to a seventh aspect.Like parts have like numbers and functions as the sensor assembly 9shown in FIGS. 1 to 19 with the addition of decimal extension “0.6”.Assembly 9.6 is substantially the same as assembly 9 shown in FIGS. 1 to19 with the following exceptions.

As seen in FIG. 29, sensor assembly 9.6 includes a first subassembly inthe form of an RFID tag 10.6 in this example.

Sensor 14.6 includes an RFID reader 101 mounted on circuit board 20.6.Radio 28.6 and antenna 30.6 allow the sensor to communicate with acontrol panel 102 as part of a wireless security alarm system 31.6.There is a wire 104 in this example which may be electrically andreleasably connected to the sensor 14.6. The wire allows the sensor tocommunicate with the control panel 102 as part of a wired security alarmsystem. The sensor 14.6 communicates with the control panel toselectively trigger an alarm.

The RFID tag 10.6 and the sensor 14.6 are used as a window sensor forwindow 50.6 seen in FIGS. 30 to 32 in this example in a firstconfiguration of security alarm system 31.6; however this is notstrictly required and the sensor assembly 9.6 may be used in othermanners in other examples. In a wireless security alarm system 31.6configuration the sensor 14.6 is mounted on stile 52.6 of window 50.6and RFID tag 10.6 is mounted on side jamb 54.6 of the window near sill56.6 thereof. In a wired configuration the RFID tag is mounted on thestile of window and the sensor is mounted on the side jamb of the windownear sill thereof.

Referring to FIG. 30, the window is fully closed with bottom rail 58.6of the window abutting the sill thereof. The sensor 14.6 seen in FIG. 29is configured to read the RFID tag 10.6 when the window 50.6 is fullyclosed, and signals that the window 50.6 is closed. A signal is thussent by the RFID reader 101 to the microprocessor 22.6 when the RFIDreader is in communication range with the RFID tag in one example.Indicator 16.6 indicates when data from the RFID tag 10.6 has beentransmitted to the RFID reader 101 in response to the RFID tag beingtriggered by electromagnetic interrogation from the RFID reader. Theindicator thus indicates when the RFID reader 101 in communication rangewith the RFID tag 10.6 and data from the RFID tag is received by theRFID reader, and turns off when the RFID tag is not detected and not incommunication range in one example.

In addition or alternatively and still referring to FIG. 29, themicroprocessor is configured to analyze changes in signals from the RFIDtag to determine when a distance between the RFID tag and the RFIDreader is within a predetermined threshold. This may be determined bythe microprocessor 22.6 analyzing and comparing changes in time andamplitude characteristics of the signals, for example. In this case theindicator 16.6 indicates when the distance between the RFID tag 10.6 andthe RFID reader 101 is within a predetermined threshold. In this casethe indicator turns on when the distance between the RFID tag and theRFID reader is within said predetermined threshold and turns off whenthe distance between the RFID tag and the RFID reader is outside of saidpredetermined threshold.

Likewise, as shown in FIG. 31, the sensor 14.6 is also able to read theRFID tag 10.6 when the window 50.6 is open up to a threshold distanceD1.6. It is desirable to allow the window 50.6 to be partially openedfor ventilation but not opened enough to allow an intruder to enterthrough the window 50.6. The sensor 14.6 will accordingly not trigger analarm when the sensor 14.6 is able to read the RFID tag 10.6.

However, and with reference to FIG. 32, when the window 50.6 is open toa distance D2.6, which is greater than the threshold distance D1.6, thesensor 14.6 is no longer able to read the RFID tag 10.6 and/or themicroprocessor determines that the RFID tag is at a distance greaterthan the threshold distance, and an alarm is triggered. The sensor maybe mounted on bottom rail 58.6 of the window in other configurations,for example.

FIG. 33 shows a sensor assembly 9.7 according to an eighth aspect. Thesensor assembly is substantially similar to the sensor assembly 9.6 ofFIGS. 29 to 32, with like parts having like numbers and functions withdecimal extension “0.7” replacing “0.6” and decimal extension “0.7”being added for numbers not previously having decimal extensions, withthe following exception. Sensor assembly 9.7 includes a pull strip 90.7to selectively enable a power source thereof to power the sensor 14.7thereof in a manner substantially similar to that described for sensorassembly 9.5 seen in FIGS. 25 to 28.

It will be understood by a person skilled in the art that many of thedetails provided above are by way of example only, and are not intendedto limit the scope of the invention which is to be determined withreference to the following claims.

What is claimed is:
 1. A magnetic field sensor comprising: a housinghaving a lid; a tamper switch which detects when the lid of the housingis opened; a device which senses a presence or an absence of a magneticfield; a power source disposed within the housing; a pull strippositioned to inhibit the power source from providing power to themagnetic field sensor, with the magnetic field sensor being powered upwhen the pull strip is removed from the power source; a microprocessor,a signal being sent by the tamper switch to the microprocessor when thelid of the housing is open, and a signal being sent by the device to themicroprocessor when a magnetic field is sensed; and an indicator whichindicates the presence or the absence of a magnetic field, wherein thepower source supplies current to the indicator, and the indicator turnson when a magnetic field is sensed and turns off when a magnetic fieldis not sensed; wherein the indicator is initially operable following thepull strip being removed from the power source and the magnetic fieldsensor being powered up, and the microprocessor renders the indicatorinoperable a predetermined period of time after the pull strip isremoved from the power source and the magnetic field sensor is poweredup, and the indicator remaining inoperable until the lid of the housingis removed and the lid of the housing is next closed at which point theindicator is operable until the microprocessor renders the indicatorinoperable a further said predetermined period of time after the lid ofthe housing is closed.
 2. The magnetic field sensor as claimed in claim1, wherein the indicator is a visual indicator.
 3. The magnetic fieldsensor as claimed in claim 1 wherein the indicator comprises a lightemitting diode.
 4. The magnetic field sensor as claimed in claim 1wherein the indicator is an auditory indicator.
 5. The magnetic fieldsensor as claimed in claim 1, wherein the indicator is a vibratoryindicator.
 6. The magnetic field sensor as claimed in claim 1 furtherincluding a supercapacitor.
 7. The magnetic field sensor as claimed inclaim 1 further including a radio and an antenna.
 8. The magnetic fieldsensor as claimed in claim 1 wherein the pull strip is an insulator. 9.The magnetic field sensor as claimed in claim 1 wherein the pull stripremovably couples to the power source via adhesive.
 10. The magneticfield sensor as claimed in claim 1, wherein said device is amagnetoresistive sensor.
 11. The magnetic field sensor as claimed inclaim 1, wherein said device is a Hall Effect sensor.
 12. The magneticfield sensor as claimed in claim 1 wherein the power source is a coincell battery.
 13. The magnetic field sensor as claimed in claim 1wherein the magnetic field sensor is a parallelepiped in shape.
 14. Aproximity sensor comprising a magnet and the magnetic field sensor asclaimed in claim
 1. 15. A security alarm system including the proximitysensor as claimed in claim
 14. 16. A magnetic field sensor comprising: ahousing having a lid; a tamper switch which detects when the lid of thehousing is opened; a device which senses a presence or an absence of amagnetic field; a power source; a pull strip positioned to inhibit thepower source from providing power to the magnetic field sensor, with themagnetic field sensor being powered up when the pull strip is removedfrom the power source; a microprocessor, a signal being sent by thetamper switch to the microprocessor when the lid of the housing isremoved, and a signal being sent by the device to the microprocessorwhen a magnetic field is sensed; and an indicator which indicates thepresence or the absence of a magnetic field, wherein the power sourcesupplies current to the indicator, and the indicator turns on when amagnetic field is sensed and turns off when a magnetic field is notsensed; wherein the indicator turns on following the pull strip beingremoved from the power source and when a magnetic field is sensed, theindicator remaining on for a predetermined period of time while themagnetic field is sensed and the lid of the housing is closed, and theindicator then being turned off, even if a magnetic field is sensed,until the lid of the housing is removed to restart an algorithm based onthe signal sent by the tamper switch to the microprocessor when the lidof the housing is removed, the algorithm relating to the sensing of amagnetic field.
 17. The magnetic field sensor as claimed in claim 16wherein the pull strip is an insulator.
 18. The magnetic field sensor asclaimed in claim 16, wherein said device is a magnetoresistive sensor ora Hall Effect sensor.
 19. The magnetic field sensor as claimed in claim16 wherein the power source is a coin cell battery.
 20. A magnetic fieldsensor comprising: a housing including a lid and a tamper switch whichdetects when the lid thereof is removed; a device which senses apresence or an absence of a magnetic field; a microprocessor, a signalbeing sent by the tamper switch to the microprocessor when the lid ofthe housing is removed, and a signal being sent by the device to themicroprocessor when a magnetic field is sensed; and an indicator whichindicates the presence or the absence of a magnetic field, the indicatorturning on upon both being powered up and a magnetic field being sensed,the indicator remaining on for a predetermined period of time while themagnetic field is sensed and the lid of the housing is closed, and theindicator then being turned off, even if a magnetic field is sensed,until the lid of the housing is removed to restart an algorithm based onthe signal sent by the tamper switch to the microprocessor when the lidof the housing is removed, the algorithm relating to the sensing of amagnetic field.